Methods and systems for measuring and monitoring solutions are known and involve a wide variety of techniques. For example, Hagedora U.S. Pat. No. 4,226,114 describes a method of analysis which is based upon measurement of change of enthalpy. Williams U.S. Pat. No. 4,680,271 uses continuous differential colorimetric analysis. Both of these systems are based on techniques which require certain physical or chemical changes to take place, are relatively complex and are apparently limited to use in connection with compounds which are highly soluble in the solvent in which they are measured. In the field of compounds of limited solubility in a solvent, especially gypsum (calcium sulfate dihydrate) in water, particularly when several other chemical components are present, it has heretofore been extremely time consuming to measure the degree of saturation or relative saturation of the compound of interest in the solvent. Measuring relative saturation of a desired component of limited solubility is important in industry because, when such a solution becomes supersaturated with respect to a particular component, e.g. in a process in which the solution is evaporated, the component of limited solubility tends to come out of solution and to deposit on surfaces of processing equipment (scaling), which leads to plugging and heat-tranfer losses and eventually to shutdowns, with concurrent loss in operating time. Two possibilities exist for a solution not in equilibrium with respect to a given compound, either the solution is subsaturated or it is supersaturated. The relative saturation is defined as being less than one in the subsaturated case and greater than one when supersaturated.
In the field of gypsum-in-water solutions, encountered for example in certain gas desulfurization processes, wherein the solutions are evaporated, present techniques for determining the degree of saturation of gypsum in such complex aqueous solutions are, as mentioned, extremely time consuming. For example, two approaches presently used to determine the degree of saturation or relative saturation in solutions of this character are 1) complete chemical analysis of the solution followed by use of a computerized computational scheme, or 2) chemical analysis for calcium and sulfate, equilibration with gypsum solids, and a reanalysis after equilibration. Both of these techniques require significant analytical capability and involve from four to eight hours to complete